<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			/*选择父元素的第一个p儿子并且该儿子是父元素的第一个儿子。*/
			div > p:first-child	{
				width: 400px;
				height: 30px;
				background-color: paleturquoise;
			}
		</style>
	</head>
	<body>
		<div >
			<p>ppppppp</p>
			<span>span</span>
			<p>ppppppp</p>
			<p>ppppppp</p>
			<p>ppppppp</p>
		</div>
	</body>
</html>
